Labour's leadership battle has intensified as Jeremy Corbyn and Tom Watson entered a war of words over the deputy leader's claims that "Trotsky entryists" were manipulating young party members.

Publicly, the pair's relationship has remained relatively peaceful despite Mr Watson telling Mr Corbyn he should stand down after 172 MPs backed a no-confidence motion in the leader.

But Mr Corbyn's campaign team reacted furiously after Mr Watson accused "Trotsky entryists" of returning to the Labour Party and manipulating younger members to boost the leader's chances of staying in post.

The falling-out came as Andy Burnham won the race to be Labour's candidate for Greater Manchester mayor in a 2017 election he will be widely expected to win, given the party's support in the city.

But shortly after his victory Mr Burnham found himself defending rebel MPs against a threat of mandatory reselection from one of the new pro-Corbyn members of the ruling National Executive Committee (NEC).

It came as Mr Watson suggested "Trots" are attempting to use Labour as a "vehicle for revolutionary socialism", are not "remotely interested in wining elections" and do not have the "best interests of the Labour Party at heart".

The deputy leader insisted he does not believe the vast majority of people who have joined the party and have been mobilised by the pro-Corbyn Momentum campaign group "are all Trots and Bolsheviks".

He told The Guardian: "Some of these people are deeply interested in political change, in building a more equal society, and are just on a journey in politics that they're new to, and I don't want them to feel that I'm labelling them because I'm not.

"But there are some old hands twisting young arms in this process, and I'm under no illusions about what's going on.

"They are caucusing and factionalising and putting pressure where they can, and that's how Trotsky entryists operate. Sooner or later, that always end up in disaster."

A Jeremy for Labour spokesman accused Mr Watson of orchestrating the party's appeal against a High Court ruling that new Labour members should be allowed to vote in the leadership election - an apparent boost to Mr Corbyn.

The spokesman said: "We regret that Tom Watson also forced through the decision yesterday at Labour's NEC meeting to challenge the court judgment to restore the right to vote in the leadership election.

"Rather than patronising members and peddling baseless conspiracy theories about 'Trotsky entryists', he should be working with Jeremy to unite our party so that we can get back to campaigning to dislodge this Tory Government, and help elect a Labour government in its place."

Rhea Wolfson, one of a slate of left-leaning new NEC members, appeared to threaten anti-Corbyn MPs with mandatory reselection to address the "important disconnect" between the parliamentary party and rank-and-file members.

She told BBC Radio 4's World At One: "Ultimately we have to have a much more healthy conversation around reselection, if not mandatory reselection."

But Mr Burnham said her comments were unhelpful and would only fuel a climate of distrust.

The shadow home secretary told the programme: "To pull the rug from under our MPs or other elected representatives, I don't think is helpful at this time. It fuels a climate of distrust and I don't think that that is where we should be."

Meanwhile, former leader Ed Miliband backed Owen Smith to oust Mr Corbyn at the top of the party.

Mr Corbyn has previously described Mr Miliband as a "great friend" and he was consistently rumoured to be joining the current leader's shadow cabinet.

But Mr Miliband said Mr Smith is the best candidate to make the crisis following the EU referendum "a progressive moment".

"I want a Labour leader who can rise to the challenge of this moment," he said.

"I want a Labour leader who can unite our party and make us a serious alternative government.

"And I want a Labour leader who will reach out to every part of Britain and can do what Labour has done in the past, which is out of this crisis make it a progressive moment.

"That's why my choice for Labour leader is Owen Smith."

Responding to the comments by the Jeremy for Labour campaign, Mr Watson said: " In my interview with The Guardian I made it clear that many members of Momentum are motivated by a desire to see political change and build a more equal society.

"John McDonnell has consistently made it clear that everyone in our party must be free to express their opinion and be heard respectfully without fear of being shouted down, which is why I simply don't believe he approved these intemperate words from Jeremy's campaign."

Mr Burnham defended his neutral stance in the Labour leadership battle, after a former ally hit out at him.

Labour MP Michael Dugher, a key supporter in Mr Burnham's own bid for leader last summer, tweeted: "What did I do in the war, son?

"Oh I remained neutral."

Responding to the criticism, the Manchester mayoral hopeful insisted he is in a "different position" to other MPs because he pledged to support Mr Corbyn after losing to him last year.

He told Channel 4 News: "Talking about a war... is that really what people want here? Is that really what they think is in the best interests of our party? Talking about us in that way.

"In the end if you're not careful one side wins over the other and that leads to a split."

He added: "I'm in a different position to the rest of the Parliamentary Labour Party. I would expect people to respect that.

"I've never taken part in the civil wars we've seen in the party. I didn't do it against Tony Blair, I didn't do it against Gordon Brown, I didn't do it against Ed Miliband.

"I always put the unity of our party first, so that's the way I've done my politics."